The present invention relates generally to an improved conveyor positioner system for flexible plastic film products, and particularly a high speed conveyor for handling flexible plastic film products as they are sequentially delivered in non-captive form from a web converting apparatus such as a flexible plastic film bag-making machine or the like. Bagmaking machines for the fabrication of film products from polyethylene are examples of such apparatus, and are in common usage in the art.
As the speed of the web converting apparatus increases, the problem of handling the flexible plastic film products increases significantly, and particularly the handling of the product as it is delivered or discharged from the apparatus. While various techniques have been and are being used for controlling the handling and positioning of flexible plastic film products as they are delivered from a converting apparatus, problems continue to exist with respect to repeatability of product placement, and also with respect to the delivery of film products in repeatable and controlled form.
The fabrication or conversion of plastic material into individual products such as bags is commonplace. Such bags, normally formed of polyethylene, have a wide variety of applications. In certain instances, the user of certain larger size bags employs a wicket pin for retention of a quantity of individual bags in a stack, with the bags normally containing uniform perforations or holes at or along one of the ends, such as along an upper lip extension. The presentation and disposition of the bag product during loading onto the wicket member presents delivery problems, since the individual bags, upon delivery from the converting equipment, must be uniformly placed upon a stacker input station for ultimate delivery to the wicket member. Stacker apparatus which has been used in the past is disclosed in U.S. Reissue Pat. No. 27,523 and U.S. Pat. No. 3,921,827, with such stacking apparatus employing a rotary hub carrying bag retaining arms for receiving the individual bags at a stacker input station, for ultimate delivery onto a wicket member.
As can be appreciated, the problems encountered with handling the plastic film products such as bags increase significantly as machine speed is increased. Plastic film products are exceedingly difficult to handle at high rates of speed because of the inherent flimsiness of the film material and the inherent viscosity of the ambient air. The film products become distorted, fold, or flex so that uniform pick-up and later delivery to the ultimate disposition may be adversely affected, the later delivery being dependent upon the accuracy at which the product may be delivered to the input station. In other words, any misalignment, folding or other anomalies in the form of the product will be reflected in adverse stacking conditions and may result in a jamming situation, damaged product, or an unattractive arrangement of finished product.
In order to assist in controlling the positioning of the film product as it leaves a captive conveyor, and enters the stacker input station, it has been found that control of the positioning may be enhanced by utilization of the Bernoulli effect. The pressure of a flowing stream of gaseous fluid is effectively reduced as its speed of flow is increased. This phenomena has generally been known as the "Bernoulli effect", and may be derived theoretically from the Bernoulli Theorem. It is this phenomena which is utilized to reduce the pressure in the stream of gaseous fluid beneath the plane of the flexible plastic film article so as to draw the article down and into partial or floating contact with a stationary receiving platen or platform. In order to achieve an affect from the pressure drop, this platform must be, of course, discontinuous so as to expose the flexible plastic film article to the zone of reduced pressure. Accordingly, a grid-work arrangement may be effectively utilized as the receiving surface and stacker input station for flexible plastic film articles or products upon discharge or release from a moving conveyor. While a stationary grid is ordinarily preferred, in certain applications, a series of endless belts may be utilized, with these belts being driven at a predetermined speed so as to provide a moving platform. In certain other applications, it may be desirable to employ a combination of moving endless belts and a stationary grid, with the grid, in such a situation, providing a datum plane controlling horizontal downward movement of the product.
In order to achieve the Bernoulli effect, the nozzles utilized for the discharge of compressed gaseous fluid, such as air, are arranged to have their orifices direct the gas flow along a line or axis generally parallel to the direction of motion or travel of the film article. Since the platen or platform for receiving the articles is disposed along a plane which is above the plane of the discharge orifices, the reduction in pressure due to the Bernoulli effect overcomes the tendency of the moving stream of air to adversely affect the stability during travel of the plastic film article, and hence the article will normally lie flat upon the surface of the grid for pick-up by the stacker device. Thus, a relatively smooth, predictable, and repeatable path is followed by the plastic film product, thereby rendering the pick-up and subsequent placement of the product or article highly reliable.
In addition to the gaseous discharge means providing the Bernoulli effect in a plane beneath the film articles, a second set of orifices is normally provided in order to assist in control of the motion or travel of the articles. Specifically, a second set of orifices may be provided along or adjacent the hot knife, with these orifices delivering a constant flow of gaseous fluid onto the upper surface of the film articles. The specific arrangement of the second set of discharge orifices will be described in greater detail hereinafter.
The arrangement of the present invention is particularly adapted for those rotary stackers previously mentioned, such as described in U.S. Pat. No. 3,921,827. Such devices are particularly useful for handling plastic film products which have a pair of spaced bores or holes formed therein for ultimate placement upon a wicket device. In this connection, the rotary stacker device will have pairs of arms extending radially outwardly from a central core, with these arms being, of course, spaced radially parallelly, one to another, outwardly from the core. The grid or other surface for receiving the plastic film products will normally be spaced between the opposed radially extending arms, with the arms being arranged, therefore, to pick up articles as deposited upon the grid.
The utilization of a discharge of compressed gaseous fluid, such as air, provides a greater degree of stability for the film products carried on the rotary stackers as described in U.S. Pat. No. 3,921,827. Specifically, a pressure reduction occurs at the trailing surface of a film product as it moves in its orbital path, and the discharge of compressed gaseous fluid into this zone replenishes, equalizes, or stabilizes the air in the zone, and this pressure equalization has been found to provide additional assistance in positioning of the film article upon the receiving platen or platform. This beneficial affect is one which may not reasonably be expected if a partial vacuum were utilized to exercise control over the movement of the film article.